We've removed the dark theme. Light theme is the future.
Before you get really angry, try to understand this from a development point of view: it's a lot of work to maintain two distinct themes. If you haven't noticed, we don't develop for the dark theme...
For example, the inbox "compose message" page hasn't been themed for the dark theme. The input boxes have just been white since the release of the inbox.
Thanks for understanding.
April Fools. You guys suck.